Prevention of Zinc Precipitation with Calcium Phosphate by Casein Hydrolysate Improves Zinc Absorption in Mouse Small Intestine ex Vivo via a Nanoparticle-Mediated Mechanism

J Agric Food Chem. 2020 Jan 15;68(2):652-659. doi: 10.1021/acs.jafc.9b07097. Epub 2020 Jan 7.

Abstract

Casein phosphopeptides are known to enhance zinc absorption, but the underlying mechanism remains unclear. Here, a gastrointestinal casein hydrolysate (CH) was found to keep zinc in solution despite heavy precipitation of calcium and phosphate, the omnipresent mineral nutrients that could co-precipitate zinc out of solution instantly and almost completely under physiologically relevant conditions. Dynamic light scattering, transmission electron microscopy, and energy-dispersive X-ray analysis displayed the CH-mediated formation of zinc/calcium phosphate (Zn/CaP) nanocomplexes aggregated from rather small nanoclusters. The ex vivo mouse ileal loop experiments revealed enhanced intestinal zinc absorption by CH's prevention of zinc co-precipitation with CaP, and the treatments with specific inhibitors unveiled the involvement of macropinocytic internalization, lysosomal degradation, and transcytosis in the intestinal uptake of zinc from Zn/CaP nanocomplexes. A low calcium-to-phosphorus ratio adversely affected CH's efficiency to enhance zinc solubility and absorption. Overall, our study provides a new paradigm for casein phosphopeptides to improve zinc bioavailability.

Keywords: calcium phosphate precipitation; casein phosphopeptides; macropinocytosis; nanocomplexes; zinc bioavailability.

MeSH terms

  • Animals
  • Biological Availability
  • Calcium Phosphates / chemistry*
  • Calcium Phosphates / metabolism
  • Caseins / chemistry*
  • Caseins / metabolism
  • Intestinal Absorption
  • Intestine, Small / metabolism*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Nanoparticles / chemistry
  • Nanoparticles / metabolism
  • Zinc / chemistry*
  • Zinc / metabolism*

Substances

  • Calcium Phosphates
  • Caseins
  • casein hydrolysate
  • calcium phosphate
  • Zinc